The intervertebral discs, which are located between adjacent vertebrae in the spine, provide structural support for the spine as well as the distribution of forces exerted on the spinal column. An intervertebral disc consists of three major components: cartilage endplates, nucleus pulposus, and annulus fibrosus.
In a healthy disc, the central portion, the nucleus pulposus or nucleus, is relatively soft and gelatinous; being composed of about 70% to about 90% water. The nucleus pulposus has high proteoglycan content and contains a significant amount of Type II collagen and chondrocytes. Surrounding the nucleus is the annulus fibrosus, which has a more rigid consistency and contains an organized fibrous network of about 40% Type I collagen, about 60% Type II collagen, and fibroblasts. The annular portion serves to provide peripheral mechanical support to the disc, afford torsional resistance, and contain the softer nucleus while resisting its hydrostatic pressure.
Intervertebral discs, however, are susceptible to disease, injury, and deterioration during the aging process. Disc herniation occurs when the nucleus begins to extrude through an opening in the annulus, often to the extent that the herniated material impinges on nerve roots in the spine or spinal cord. The posterior and posterolateral portions of the annulus are most susceptible to attenuation or herniation, and therefore, are more vulnerable to hydrostatic pressures exerted by vertical compressive forces on the intervertebral disc. Various injuries and deterioration of the intervertebral disc and annulus fibrosus are discussed by Osti et al., Annular Tears and Disc Degeneration in the Lumbar Spine, J. Bone and Joint Surgery, 74-B(5), (1982) pp. 678-682; Osti et al., Annulus Tears and Intervertebral Disc Degeneration, Spine, 15(8) (1990) pp. 762-767; Kamblin et al., Development of Degenerative Spondylosis of the Lumbar Spine after Partial Discectomy, Spine, 20(5) (1995) pp. 599-607.
Many treatments for intervertebral disc injury have involved the use of nuclear prostheses or disc spacers. A variety of prosthetic nuclear implants are known in the art. For example, U.S. Pat. No. 5,047,055 (Bao et al.) teaches a swellable hydrogel prosthetic nucleus. Other devices known in the art, such as intervertebral spacers, use wedges between vertebrae to reduce the pressure exerted on the disc by the spine. Intervertebral disc implants for spinal fusion are known in the art as well, such as disclosed in U.S. Pat. No. 5,425,772 (Brantigan) and U.S. Pat. No. 4,834,757 (Brantigan).
Further approaches are directed toward fusion of the adjacent vertebrate, e.g., using a cage in the manner provided by Sulzer. Sulzer's BAK® Interbody Fusion System involves the use of hollow, threaded cylinders that are implanted between two or more vertebrae. The implants are packed with bone graft to facilitate the growth of vertebral bone. Fusion is achieved when adjoining vertebrae grow together through and around the implants, resulting in stabilization.
Apparatuses and/or methods intended for use in disc repair have also been described for instance in French Patent Appl. No. FR 2 639 823 (Garcia) and U.S. Pat. No. 6,187,048 (Milner et al.). Both references differ in several significant respects from each other and from the apparatus and method described below.
Prosthetic implants formed of biomaterials that can be delivered and cured in situ, using minimally invasive techniques to form a prosthetic nucleus within an intervertebral disc have been described in U.S. Pat. No. 5,556,429 (Felt) and U.S. Pat. No. 5,888,220 (Felt et al.), and U.S. Patent Publication No. US 2003/0195628 (Felt et al.), the disclosures of which are incorporated herein by reference. The disclosed method includes, for instance, the steps of inserting a collapsed mold apparatus (which in a preferred embodiment is described as a “mold”) through an opening within the annulus, and filling the mold to the point that the mold material expands with a flowable biomaterial that is adapted to cure in situ and provide a permanent disc replacement. Related methods are disclosed in U.S. Pat. No. 6,224,630 (Bao et al.), entitled “Implantable Tissue Repair Device” and U.S. Pat. No. 6,079,868 (Rydell), entitled “Static Mixer”, the disclosures of which are incorporated herein by reference.
FIG. 1 illustrates an exemplary prior art catheter 11 with mold or balloon 13 located on the distal end. In the illustrated embodiment, biomaterial 23 is delivered to the mold 13 through the catheter 11. Secondary tube 11′ evacuates air from the mold 13 before, during and/or after the biomaterial 23 is delivered. The secondary tube 11′ can either be inside or outside the catheter 11.